Arduino string comparison not working when using String str_out = String((char*)buf); - c++

Question

I am successfully receiving data over RF on a second Arduino. However I am trying to compare the incoming string so that I can call a method when there is a match. The "if" block is never executed. I am just trying to compare the strings that are incoming. It's printing the correct values to the serial monitor but the block is never executed. Maybe because this is using a pointer to a string (don't shoot me)? I am not that familiar with C or C++. I have tried several of the string comparison methods in the Arduino docs but no joy? Any reccomendations?
void loop()
{
// Set buffer to size of expected message
uint8_t buf[7];
uint8_t buflen = sizeof(buf);
// Check if received packet is correct size
if (rf_driver.recv(buf, &buflen))
{
// Message received with valid checksum
Serial.print("Message Received: ");
String str_out = String((char*)buf);
Serial.println(str_out); /
if (str_out == "plasma1") { // this is never executed wtf!!!
plasmaSequenceOne();
} else if (str_out == "plasma2") {
plasmaSequenceTwo();
} else if (str_out == "plasma3") {
plasmaSequenceThree();
} else if (str_out == "plasma4") {
plasmaSequenceFour();
}
}
}

Answer 1

Making Alex' self-response easier readable, and avoiding unnecessary String objects:
uint8_t buf[8];
uint8_t buflen = sizeof(buf)-1; // leave space for terminating 0
if (rf_driver.recv(buf, &buflen)) {
buf[buflen] = 0;
char* str_out = (char*)buf;
Serial.println (str_out);
if (strcmp(str_out, "plasma1")==0) plasmaSequenceOne();
...
}
This worked, thanks to #Remy Lebeau.